1. Field of the Invention
This invention relates generally to the field of sterilizing and cleaning tubular structures including long, narrow, tubular structures. In particular, it relates to a device and method for cleaning and sterilizing medical devices with lumens.
2. Description of the Related Art
Many tubular structures, in particular flexible fiber endoscopes, define long tortuous lumens. These lumens are typically from about 1 m to about 4 m long with inside diameters from about 0.5 mm to about 6 mm and frequently contain crevices, bends, connections, restrictions, and irregularities. These instruments are frequently used in diagnostic medicine, requiring penetration into the human body or other contact with the human bloodstream. It is, therefore, desirable that they are cleaned, rinsed, sterilized, disinfected, or otherwise treated with fluid chemical disinfectants or sterilants to prevent the cross contamination and transmission of pathogenic organisms from patient to patient. In order for fluid chemical sterilization to be effective, the chemical must reach all internal and external surfaces. Efficaciousness, therefore, is severely limited by the inherent irregularities present in the long, narrow, lumens of flexible fiber endoscopes making effective cleaning and sterilization difficult.
Consistently and quickly cleaning, disinfecting, and sterilizing medical devices is an important part of providing quality healthcare. Failure to consistently clean and sterilize medical instruments leads to unwanted transmission of bacteria, viruses, and other organisms to and from patients. Improper handling of medical instruments allows unwanted organisms access inside the body where they may cause infection and disease.
Although the terms "sterilization" and "disinfection" are sometimes used imprecisely, the medical industry and regulatory agencies have more precisely defined the following terms including subdividing disinfection into high, intermediate, and low level disinfection.
Sterilization is generally defined as the destruction or elimination of all microbial life forms. Operationally, a sterilizing process is one that destroys all microbes on a device that has been contaminated with 10.sup.6 bacterial endospores.
High level disinfection is generally defined as the destruction or elimination of all microbial life forms except microbial spores. High level disinfectants however, must show a capability of destroying bacterial spores over an extended period of time.
Intermediate disinfection is generally defined as the destruction of all microbial life forms except bacterial spores and some viruses. However, intermediate disinfection requires the destruction or elimination of Mycobacterium tuberculosis var. bovis, which is a relatively difficult bacterium to destroy.
Low level disinfection is generally defined as the destruction of vegetative forms of bacteria (such as salmonellae and staphylococci), most fungi, medium sized or lipid containing viruses (such as herpes simplex virus, hepatitis B virus, and HIV), but not bacterial endospores, mycobacteria, or small or non-lipid viruses (such as poliovirus and rhinovirus).
The level of disinfection or sterilization desired for a particular piece of equipment generally depends on the degree of exposure the equipment poses to the patient. For example, sterilization is generally necessary for equipment that is introduced directly into the human body, either in contact with the blood stream, or in contact with normally sterile areas of the body. High level disinfection is generally required for equipment that contacts mucous membranes, but does not penetrate bodily surfaces. Low and intermediate disinfection is generally required for equipment that contacts unbroken skin.
Endoscopes, which are used to probe internal passages of the body, are an exception to the general rule of sterilizing equipment that is introduced directly into the human body. Ideally, all endoscopes should be cleaned and sterilized between uses. However, due to their delicate optical equipment, endoscopes remain an exception to the sterilization rule. The delicate optical equipment and lenses in these devices do not allow conventional methods of sterilization such as autoclaving, ethylene oxide gassing, or soaking for several hours in liquid sterilants. Autoclaving requires high temperatures for sterilization, which damages the optical lenses of the endoscopes. Ethylene oxide gas equipment is expensive and requires several hours to complete the sterilization and degassing process. Repeated soaking in liquid sterilants may also damage some endoscopes. In addition, the high cost of these specialized pieces of equipment demands efficient utilization of the instruments, requiring use of the same endoscope on as many patients in as little time as feasible. Therefore, soaking in liquid sterilants or sterilization by ethylene oxide gas is not economically feasible because of the long time period required. The demand for rapid reuse results in pressure to shorten or eliminate cleaning, disinfection, and sterilization practices. As a compromise to all of these considerations, high level disinfection for endoscopes is conventionally accepted in lieu of sterilization.
Although high level disinfection has been conventionally acceptable, it does not provide the level of safety of sterilization. The conventional rationale for accepting the reduced level of safety is that endoscopes contact mucous membrane and do not provide access to the blood stream. However, endoscopes are routinely used to find lesions in mucous membrane areas that may provide access to the blood stream. In addition, many endoscopes provide biopsy forceps that are miniature scalpels used to cut biopsy samples from the mucous membrane tissue. These common practices provide access to the bloodstream and a potential pathway for unwanted organisms to access all parts of the body. In addition to providing a direct path to the bloodstream, many endoscopes such as duodenoscopes are used in normally sterile parts of the body. Introducing contaminated equipment into these areas has been shown to cause infection.
The lumens of medical devices have conventionally been difficult to clean, disinfect, and sterilize. Some larger lumens may be cleaned with brushes. However, lumens that are too small for brushes are generally limited to cleaning by flushing with fluids such as water or air. As noted previously, the lumens also contain crevices, bends, connections, restrictions, and irregularities that restrict flow and hold residual material making cleaning difficult. Before a piece of equipment is disinfected or sterilized, it is preferably first cleaned. Failure to completely clean residual material from the equipment potentially leaves microorganisms within and beneath the residual material not easily accessible to the disinfectant or sterilant.
Some conventional devices have used special attachments or caps to direct flow into different passages of endoscopes. However, these attachments create additional attachment points. The unexposed surfaces between the attachment and the medical device may not receive complete cleaning or sterilization.
Typically, conventional devices and methods of cleaning have used unidirectional flow to clean long narrow devices with lumens. It is believed that irregularities and restrictions in the passages create air pockets or sheltered areas along the passages. For example, as the fluid flows around corners, the fluid tends to flow to the outside of the corner, leaving an air pocket or undisturbed liquid or material on the inside edge. Fluid flow is also reduced on the downstream side of any restriction.
Some devices, such as those disclosed in Ishii 4,526,623, use suction from a syringe to draw residual fluid in the lumens or to draw fluid from an additional fluid container.
However, the use of suction may collapse lumens, introduce additional air pockets in the lumen, and create the need for additional attachments. Suction may also require the use of check valves to properly control the removal of fluid and reduce the amount of air introduced into the medical device. Check valves may also reduce or eliminate complete removal of the fluid. Cleaning by suction only removes liquid from multiple lumens until one lumen contains air. Once a single lumen contains air, only air is drawn through the device because air flows more easily than liquid. The relative differences in the size of the lumens would also cause certain lumens to drain more quickly, leaving liquid in the remaining lumens. Lastly, the syringe method and device of Ishii is not easily automated.
Sterilization methods have also included immersion or soaking of medical devices in liquid sterilant. Sterilization by soaking typically requires several hours and air bubbles may become trapped inside the lumens, causing inconsistent results.
A new and useful device and method is needed that overcomes the problems associated with conventional methods of cleaning and sterilizing tubular structures, including long, narrow, tubular structures, particularly medical devices with lumens, by providing a device and method that provides a reverse flow through the tubular structures.